1. Field of the Invention
The present invention relates to an electric centrifugal fan used for blowing air.
2. Description of the Related Art
Centrifugal fans are conventionally used for cooling devices in various electronic devices. The centrifugal fans include an impeller having a plurality of blades inside a housing, and draw air in an axial direction parallel to a rotation axis of the impeller and discharge the air in a radial direction perpendicular to the axial direction. The housing usually includes a housing body having a bottom on which a motor is secured and a sidewall which defines a passage of an air flow together with the impeller, and a housing cover closing a top of the housing body. The housing body and the housing cover are formed by resin molding. For the housing cover, the use of material excellent in heat radiation other than the resin, such as aluminum, has been proposed (see Japanese Laid-Open Patent Publication No. 2001-241395, [0043]).
In recent years, demands for size reduction for centrifugal fans have increased with size reduction of electronic devices on which the centrifugal fans are to be mounted. To reduce the size of the centrifugal fans, it is necessary to not only reduce the number of components of the centrifugal fans but also make the housing have additional functions the conventional centrifugal fans did not have. For example, U.S. Pat. No. 5,699,854 describes holding of lead wires between the housing body and a downward protrusion formed on the housing cover.
In a case of forming the entire housing by resin molding, the sidewall of the housing has to have a certain thickness in order to obtain a required strength. It is therefore difficult to reduce the size of the housing, while ensuring a large passage for an air flow formed between the impeller and the sidewall of the housing and keeping an air flow rate at an adequate level.